PRINCIPLES OF TOXICOLOGY

368 PROPERTIES AND EFFECTS OF ORGANIC SOLVENTS
engineering controls, and adequate work practices can be instrumental in limiting exposures, but
careless or inexperienced handling of solvents may still occur not only in small facilities (e.g.,
automobile paint and body shops, metal fabricators) but also may be a problem during short-term
activities in large and otherwise well-run factories and service industries. Methods that may be used
for the characterization and quantification of occupational exposure history are discussed in greater
detail in Chapters 18,19, and 21.
16.2 BASIC PRINCIPLES
The breadth of structural variability and the range of physicochemical properties exhibited by organic
solvents limits the number of generalized observations that can be made regarding physiological effects
and exposure hazards. However, because of their common industrial, commercial, and household use,
often in large quantities, it is useful to discuss some fundamental characteristics that are common to
at least the principal classes of organic solvents. Table 16.1 summarizes selected important physicochemical
properties for a number of the solvents that are discussed in subsequent sections of this
chapter. Of particular interest are the properties of volatility (vapor pressure) and water solubility, as
well as organic carbon partition coefficients, since these attributes greatly influence exposure potential
and environmental behavior.
Occupational guidelines, which are designed to control exposures to solvents and other materials
in the workplace, may be expressed in units of volume:volume [e.g., parts per million (ppm)], or in
units of mass:volume [e.g., milligrams per cubic meter (mg/m 3 )]. For vapors and gases, these data if
expressed in either form may be interconverted according to the following expression:
Y mg / m3
X ppm =
MW 24.45
where X ppm = concentration in units of volume:volume
Y mg/m 3 = concentration in units of mass:volume
MW = molecular weight of the chemical
24.45 = molar volume of an ideal gas at standard temperature and pressure.
Rearranging this expression provides the opportunity to convert in the other direction as well.
Y mg / m 3 =
(X ppm)(MW)
24.45
For purposes of dose estimation, the units of mg/m 3 are more useful since they may be used in
conjunction with inhalation rates (in units of m 3 /h or m 3 /day) to calculate chemical intake. These unit
conversion relationships do not apply for dusts, aerosols, or other chemical forms that may be airborne.
Table 16.2 presents the occupational guidelines for selected solvents and solvent constituents. These
guidelines include those developed by the American Conference of Governmental Industrial Hygienists
(ACGIH), termed threshold limit values (TLV ® ), as well as those developed by the Occupational
Safety and Health Administration (OSHA) employed as legally enforceable standards permissible
exposure limits (PELs). These guidelines and standards may be viewed as a long-term protective
concentration, represented by a time-weighted average (TWA), or a protective value for a more limited
time frame, represented by a short-term exposure limit (STEL) or a ceiling concentration. To the extent
that they are available, carcinogen classifications have been included as well. Table 16.3 provides the
definitions and differences among the available occupational guidelines. The U.S. Environmental
Protection Agency (USEPA) also has established acceptable exposure limits for many of the substances
discussed in this chapter [e.g., reference dose (RfD), cancer slope factor (CSF), and reference
concentration (RfC) for air]; however, these values are not discussed in detail as they generally do not